HEAT PUMPS | ENERGY-POSITIVE HOMES CUTTING BILLS WITH ENERGY-POSITIVE HOMES Energy-positive homes in Wales have the potential to not only reduce energy bills, but also to make money for social housing tenants. Hoare Leas Eimear Moloney Seros John Lloyd and Wales & West Housings Mark Davies describe W ith average energy bills expected to rise to more than 3,200 this October, the prospect of living in an energy-positive home has never been more attractive. This has become a reality for residents of 14 new low-cost social homes at Stormy Downs, in Bridgend, who are experiencing zero, or even negative, annual bills. The housing project was kick-started by the Welsh School of Architecture at Cardiff University, which had the goal to design and build an electric-powered home that put more energy back into the Grid than it took away. In 2017, a design team was instructed on using the Schools Smart Operation for a Low Carbon Energy Region (Solcer) concept, which was employed for the Stormy Downs homes. Rhiw Cefn Gwlad is one of 10 projects in Wales sharing 43m in the second phase of the Welsh Governments Innovative Housing Programme. The grant of 940,000 brought government investment in the scheme to 2.4m, with a further 1.4m from Wales & West Housing. The target was to accelerate industry learning on the development of sustainable social housing for the future with the aim of building 1,000 affordable homes with innovative elements, and monitoring them once occupied to understand how they performed. At Rhiw Cefn Gwlad, homes including one-bed apartments to two- or four-bedroom houses were constructed, and first occupied in January 2021. The key technologies proposed for them included photovoltaics (PVs), air source heat pumps (ASHPs) and PV solar systems (see panel, Key technologies, and Figure 1). While architecturally similar to many other housing developments, the design has additional technologies not normally seen in social housing. Each house type was designed to be energy and carbon positive over a year, putting more energy back into the Grid than it takes out. KEY TECHNOLOGIES n 3.7-7.4kW PV solar systems n 13.5kW AC-coupled lithium-ion batteries to store electricity n Pichler PKOM4 exhaust ASHPs for heating and hot water n Heating delivered through a mechanical ventilation with heat recovery (MVHR) system n Energy-efficient double-glazed windows and doors n No gas heaters, radiators or cooling 46 August 2022 www.cibsejournal.com Energy predictions In the design stage, a detailed 3D IES model was used to estimate the energy consumption and thermal performance of the homes. However, these models are not good at modelling the complex interactions between hot-water storage and varying system efficiencies, so a separate thermal-storage model was created to understand the hot-water heat pump profiles. Finally, an electrical-storage model was developed, to consider battery storage performance and optimise the battery-control strategy for the houses. Calculations were performed at half-hourly resolution over 12 months, and the models were combined to create a single model to optimise design, and create setpoint, control and energy strategies. The homes at Rhiw Cefn Gwlad include photovoltaics, PV solar systems and heat pumps